Fluid flow amplifiers, which are also called thrust jets or air flow amplifiers when the fluid is air, are pressure velocity transducers that use a small amount of a compressed fluid, e.g., compressed air, as their power source. Normally, such a device consists of two pieces. The first piece is called a body and the second piece is called a plug. The plug typically has a seal ring to seal pressurized air from leaking. The plug is screwed into the body thus forming an annular chamber and a nozzle between the body and the plug. The body has an inlet to which compressed air is introduced. As compressed air flows through the inlet, it fills the annular chamber and is then discharged through the nozzle. As the compressed air leaves the nozzle, its pressure is changed for increase in velocity. The high velocity air “adheres” to a profile, e.g., a Coanda profile of the plug, and entrains ambient air from an inlet formed by the body thus forming an air flow of high volume and speed.
Such fluid flow amplifiers are used for venting weld smoke, cooling hot parts, drying wet parts, cleaning machined parts, distributing heat in molds or ovens, or moving debris. In pending U.S. patent application Ser. No. 11/510,468 filed by the same applicants it was shown that such pressure velocity transducers can be used for driving turbomachinery to supersonic speeds. Driving turbomachinery to supersonic speeds with an air amplifier became possible because the turbomachine, which comprises mainly a compressor and a turbine, can be made of thermoplastics instead of heavy metals thus reducing inertia start-up load by a significant factor as compared to current-art turbomachinery.
Another fact that was shown concerning air-amplifier-powered turbomachinery was that, unlike an exhaust powered turbomachine, e.g., a turbocharger which gets hotter the faster it spins, an air-amplifier-powered turbocharger gets colder the faster it spins due to adiabatic cooling of compressed air.
The combination of low inertia start-up load and a cold-driven turbine cancels any excess heat of air compression. In other words, the turbine temperature is kept at or below ambient temperature such that temperature differential is kept at a minimum while still achieving high tip speeds needed for air compression. The turbine has no heat radiation. The only heat transfer occurs in the change of angular momentum of the rotating components. The aforementioned advantages allow for compressing air at a dramatically low discharge temperature as compared to current-art turbomachinery.
In a simplified form, the existing arrangements of an air amplifier that is used for venting weld smoke, cooling hot parts, drying wet parts, cleaning machined parts, distributing heat in molds or ovens, moving debris or driving turbomachinery to supersonic speeds can be illustrated by the arrangement shown in FIG. 1 below.
FIG. 1 is a simple view illustrating a known arrangement of an air flow amplifier with a ninety-degree angle discharge nozzle followed by a Coanda profile.
The arrangement shown in FIG. 1 consists of an air amplifier 10 having a body 12 and a plug 14 screwed into the rear end of the body 12 by means of a thread 13, and a lock ring 16 that is used to fasten the body 12 to the plug 14. The mating surfaces are sealed by means of an O-ring 22. At the front end of the air amplifier the body 12 and the plug 14 form an annular chamber 18 and a ninety-degree-angle nozzle 20. The body 12 has a tapered inlet 24 for access to ambient air and a transversely arranged fluid inlet 26 for the supply of a primary-flow fluid “f”. The central opening of the plug 14 forms an exhaust outlet 28, and the front end face of the plug has an air-entrapping profile 30 e.g., a Coanda profile for entraining ambient air. The Coanda effect, also known as “boundary layer attachment”, is the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. The principle was named after Romanian discoverer, who was the first to understand the practical importance of the phenomenon for aircraft development.
As a compressed fluid, e.g., compressed air (black arrows “f”), is introduced in the fluid inlet 26, it fills the annular chamber 18. The compressed fluid is then discharged through the nozzle 20 and adheres to the profile 30 which entrains the secondary fluid F, e.g., ambient air, through the inlet 24. As a result, a high-volume, high-velocity air flow AF is exhausted from the outlet 28.
Air amplifiers based on the principle described above are incorporated into different structural designs which are shown in the patents mentioned below for illustration purposes.
U.S. Pat. No. 6,243,966 issued in 2001 to Lubomirsky, et al presents an air amplifier device which has a body with two pieces which fit together and have an inner wall defining a generally cylindrical cavity with a center axis and with an entrance opening at its upper end and an exit opening at its other end. The two pieces have respective shoulders which abut to index the pieces in precise relationship radially, axially, and longitudinally. A pair of circular lips in the inner wall near the entrance opening form a venturi jet air opening through the inner wall to direct a controlled flow of air from a supply of air down into the cylindrical cavity. The lips are uniformly parallel with each other and concentric with the center axis, are closely and uniformly spaced apart for 360 degrees around their lengths and are two circular edges of the respective pieces, and are indexed to the respective shoulders of the pieces such that when the pieces are assembled the jet air opening is uniform within a fraction of a thousandth of an inch.
U.S. Pat. No. 5,402,398 issued in 1995 to Sweeney presents an air amplifier which is provided for use in pneumatic control systems that can operate over a wide range of flow and pressure characteristics, and can additionally operate against a back pressure. The air amplifier utilizes a tapered shim that causes the pressurized air to follow a Coanda profile over a wider range (and against a back pressure) than is possible when using only a slotted, non-tapered shim. The shim is ring-shaped with a planar surface and includes inwardly directed tangs that are cut-off to provide an open central area. Some or all of the tangs are tapered along either one or both sides of the tang.
U.S. Pat. No. 4,046,492 issued in 1977 to Inglis presents an air flow amplifier of relatively high air flow amplification ratios in which a thin film of pressurized primary air flowing in a transverse direction is mechanically deflected to impinge on a generally frusto-conical surface tapering towards the throat of the amplifier. The deflecting action is produced by a deflection ring which is spaced inwardly from the amplifier's annular nozzle. The ring has an internal diameter substantially larger than the amplifier's throat so that secondary air entering through the ring may flow directly towards the frusto-conical surface to mix with the primary air flowing along that surface.
Air amplifiers are designed to operate at normal shop air pressures ranging from 6.8 atm to 8.5 atm (100 psig-125 psig). Although there are some off the shelf air amplifier products that state operation of 17 atm (250 psig max), these air amplifiers cannot be operated at such pressures without extremely low gap settings ranging from 0.05 to 0.10 mm (0.002-0.004 inches). Such low gap settings results in a mediocre-performing air amplifier suitable for driving a low inertia turbocharger, for moving fumes, etc.
When operating at a gap setting of 0.23 mm (0.009 inches), the air amplifier can perform at high air consumption rates, high velocities, and maximum air entrainment. However, when pressures increase beyond 8.5 atm (125 psig), this causes flow reversal and turbulence thus resulting in a significant loss and waste of energy.
Flow reversal and turbulence occurs because at low pressures the compressed air can adhere to the designed profile, e.g., Coanda profile.
As inlet pressure to the air amplifier is increased, the velocity of the compressed air through the nozzle is increased as well, so instead of the high velocity fluid following the profile, it flows towards the center. Once the high velocity fluid reaches the center, it crashes and tumbles which results in partial air entrainment and partial energy waste.
Since air amplifiers in general are not used for driving turbomachinery, heretofore there were no demand for designing an air amplifier that could operate at high pressures, e.g., 34 atm (500 psig) or higher and at the same time could be resistant to flow reversal and turbulence. Despite the current up-to-date design, at gap settings of 0.22 mm (0.009 inches) conventional air amplifiers develop flow reversal and turbulence already at pressures much lower than 34 atm (500 psig), i.e., at 8.5 atm (125 psig).
Inventors herein tried to use shims, unique air entrainment profiles, or a combination of both to achieve maximum air entrainment, air velocity, and air consumption but still could not eliminate flow reversal and turbulence resistance when pressure exceeded 8.5 atm (125 psig) and the gaps were set at 0.22 mm (0.009 inches). An air amplifier described in above U.S. Pat. No. 5,402,398 issued in 1995 to Sweeney could overcome the above problem but only to a limited extent.
Thus, a common disadvantage of all known air amplifier devices of the aforementioned type is that they are unsuitable for use in driving turbomachinery and, if tried for such applications, are prone to flow reversal and turbulence which limit their ability to drive a turbomachine to high tip speeds.
For example, for experimental purposes the inventors herein developed a low inertia turbocharger using dual ceramic ball bearings and two Garrett T3 50 trim compressor impellers. One impeller served as a turbine because of its low weight as compared to the stock turbine, while the other compressor was used to compress air.
Two T3 0.42 air compressor housings were also used. One served to allow air compression of one of the impellers while the other housing was used as a turbine housing for the other impeller. An adjustable air amplifier model 6031 produced by Exair was used, and it was powered by a 120 cf scuba tank pressurized to 184 atm (2700 psig). The pressure was regulated down to 8.5 atm (125 psig). The gap setting on the air amplifier was set to 0.22 mm (0.009 inches). By using a flow valve, air from the scuba tank flowed through the pressure regulator to a centrifugal water separator, and then finally to the air amplifier.
A steady state tip speed of 30,000 rpm was reached, to which the impeller supplied about 50 cfm at a low pressure ratio, while the air amplifier consumed about 50-85 cfm at 8.5 atm (125 psig). Although 30,000 rpm was reached, the flow valve had to be turned on very slowly which wasted energy. Quickly turning on the flow valve resulted in uncontrollable flow reversal and turbulence which never ceased to stop or straighten out, and this decreased tip speed down to 18,000 rpm. Pressure was then increased from 8.5 atm (125 psig) psig to 17 atm (250 psig), which is the maximum rated pressure of the air amplifier. The flow valve was opened and a drastic amount of energy was lost through flow reversal and turbulence. In this case, the tip speed of 20,000 rpm was reached.
If the air amplifier could have operated without flow reversal or turbulence, tip speeds of 50000-60000 rpm could have been obtained at 17 atm (250 psig). Higher tip speeds into the 100000 rpm region at 17 atm (250 psig) could also be obtained if the impellers were made of thermoplastics, a turbine were used instead of a compressor, air bearings were used instead of a ceramic bearings, a turbine housing were used instead of a compressor housing, the compressor weres faced toward the turbine, the air amplifier were positioned closer to the turbine, and the wheels were positioned as close as possible to their designated housing. In other words, air amplifiers of known designs make it possible to reach the maximum speed of 153,500 rpm at high inlet pressures, but this can be achieve only at the expense of complicated and specific improvements that require a lot of experiments and adjustments.
After the tests stated above, the patented shim mentioned in U.S. Pat. No. 5,402,398 issued in 1995 to Sweeney was used to see if higher tip speeds would be obtained at pressures of 8.5 atm (125 psig) and 17 atm (250 psig). However, the use of the recommended shim did not produce a desired increase in speed. Instead, there was a significant drop in tip speed and air consumption. The shim stopped flow reversal and turbulence, but it choked potential air consumption, which decreased the overall kinetic energy of the air amplifier.